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Summary

Several new applications requiring solder materials that would perform for extended periods under harsh operating conditions have recently emerged. Clearly there is a need for a ROHS compliant solder with thermal and mechanical reliability better than Sn-Ag3-Cu0.5/ Sn-Ag4-Cu0.5 but with a similar melting range so that it can be a drop in replacement for these solders.

In the work shown here, Alpha focused on improving the mechanical properties of the bulk solder as well a controlled growth of interfacial IMCs and alloy microstructure. Major composition additions do impact the melting behavior and the bulk mechanical properties. Minor alloy additions can also alter the diffusion kinetics and have significant impact on the long term reliability. Tensile tests and high temperature creep tests were used for initial screening of the alloys and understanding the potential impact of each addition on the reliability of the solder in final application.

In this paper, a detailed study of the effect of small composition changes (major additions) and of micro additions is presented. Improvements in thermal, mechanical and metallurgical properties of the new alloys are discussed and compared to Sn-Ag3-Cu0.5. We show that the newly developed Pb-free solder alloy Maxrel Plus performs better than Sn-Ag3-Cu0.5 in high strain rate tests such as drop shock and vibration tests as well as in thermal fatigue tests.

Conclusions

A new Pb-free solder alloy has been developed which performs better than industry standard Pb-fee solder SAC305 in high strain rate tests such as drop shock and vibration tests as well as in thermal fatigue tests. A large number of alloys were designed, prepared and tested.

To screen the alloys, basic mechanical properties of the bulk alloy have been measured and used to predict its performance in the final real life application. Final selected candidate alloy, Maxrel Plus, has been extensively tested side by side with SAC305. Maxrel Plus performs better than SAC305 in drop shock, vibration and thermal cycling tests.

Initially Published in the SMTA Proceedings

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